Conventionally, oil injection type screw compressors are employed in various field and are still undergoing various improvements. Such improvements are directed, in addition to improvement in performance, to reduction of an occupied area and also of a size of an equipment and reduction in noise production. When it is intended to reduce the occupied area of an equipment, it is a possible resolution to employ a vertical arrangement wherein various components of an equipment, which are conventionally disposed in a plane, are otherwise disposed vertically one on another. For example, an arrangement is already known wherein a compressor body is disposed on a oil tank. Such arrangement is disclosed, for example, in Japanese Utility Model Publication Application No. 54-37444 or Japanese Utility Model Publication Application No. 52-54009.
While the occupied area of an equipment can be reduced by arranging a compressor body on an oil tank as described just above, such mere arrangement of various components in a vertical direction does not present any change of the volume occupied as a whole by the equipment. Accordingly, there remains a problem that reduction in size of the equipment is not achieved sufficiently by the solution.